AVRO-4261: [Java] Replace deprecated Class.newInstance() calls

Replace Class.newInstance() (deprecated since Java 9) with
getDeclaredConstructor().newInstance() in Perf.java and ThriftData.java.
Also remove stale 'Java 8' qualifier from SpecificCompiler javadoc.

Author: iemejia

lang/java/compiler/src/main/java/org/apache/avro/compiler/specific/SpecificCompiler.java

@@ -1225,7 +1225,7 @@ public static String generateGetMethod(Schema schema, Field field) {
   }
 
   /**
-   * Generates the name of a field accessor method that returns a Java 8 Optional.
+   * Generates the name of a field accessor method that returns an Optional.
    *
    * @param schema the schema in which the field is defined.
    * @param field  the field for which to generate the accessor name.

lang/java/ipc/src/test/java/org/apache/avro/io/Perf.java

@@ -194,13 +194,13 @@ public static void main(String[] args) throws Exception {
       String a = args[i];
       TestDescriptor t = ALL_TESTS.get(a);
       if (null != t) {
-        tests.add(t.test.newInstance());
+        tests.add(t.test.getDeclaredConstructor().newInstance());
         continue;
       }
       List<TestDescriptor> lt = BATCHES.get(a);
       if (null != lt) {
         for (TestDescriptor td : lt) {
-          tests.add(td.test.newInstance());
+          tests.add(td.test.getDeclaredConstructor().newInstance());
         }
         continue;
       }
@@ -257,7 +257,7 @@ public static void main(String[] args) throws Exception {
     if (tests.isEmpty()) {
       for (Map.Entry<String, TestDescriptor> entry : ALL_TESTS.entrySet()) {
         TestDescriptor t = entry.getValue();
-        Test test = t.test.newInstance();
+        Test test = t.test.getDeclaredConstructor().newInstance();
         tests.add(test);
       }
     }

lang/java/thrift/src/main/java/org/apache/avro/thrift/ThriftData.java

@@ -163,7 +163,7 @@ public Object newRecord(Object old, Schema schema) {
         return super.newRecord(old, schema); // punt to generic
       if (c.isInstance(old))
         return old; // reuse instance
-      return c.newInstance(); // create new instance
+      return c.getDeclaredConstructor().newInstance(); // create new instance
     } catch (Exception e) {
       throw new RuntimeException(e);
     }